The present invention relates to a resin composition for bonded magnet (bond magnet) and a bonded magnet using the same, and more particularly, to a resin composition for bonded magnet, which is excellent in moldability, and a bonded magnet using such a resin composition, which is excellent in mechanical strength and heat resistance.
As well known in the art, bonded magnets have been produced by molding a resin composition comprising a binder resin composed of thermoplastic resins such as polyamide resins and ethylene-ethyl acrylate copolymers, and magnetic particles such as ferrite particles and rare earth magnetic particles, which are mixed with the binder resin. The bonded magnets have an excellent productivity because of a light weight, a less brittleness and a good processability thereof as compared to magnets produced by a sintering method and, therefore, the bonded magnet have been used in extensive applications.
However, the bonded magnets using the binder resin composed of the above-mentioned thermoplastic resins generally show a poor heat resistance and are presently unusable in such applications requiring a high heat resistance.
When polyphenylene sulfide resins showing a relatively high heat resistance among thermoplastic resins are used as the binder resin, the obtained bonded magnets are deteriorated in productivity due to poor moldability and high brittleness thereof.
Meanwhile, the bonded magnets are generally produced by an injection-molding method or an extrusion-molding method. In the injection-molding method, sprues or runners are produced, resulting in loss of materials. To reduce the loss of materials, the thus produced sprues or runners must be recycled. However, in particular, in the case of the bonded magnets using polyphenylene sulfide resins, the recycled resins of the sprues or runners causes problems such as further deteriorated moldability and poor strength of the obtained molded products.
On the other hand, there have been proposed bonded magnets using aromatic polyamide resins having a good heat resistance as a binder resin other than the polyphenylene sulfide resins. However, the heat-resistant aromatic polyamide resins are brittle due to a high crystallinity thereof, and are deteriorated in moldability such as fluidity and recycling property as compared to ordinary aliphatic polyamides, resulting in poor handling property thereof. In order to improve the moldability, various organic additives have been added to the aromatic polyamide resins. However, almost all of these organic additives are decomposed and gasified upon molding because the molding temperature is very high, so that it may be difficult for these additives to exhibit inherent effects of improving the fluidity and preventing the deterioration in quality of resin. In addition, the use of the additives tends to cause problems such as molding defects due to gases generated therefrom and contamination of mold therewith.
Conventionally, there have been proposed various methods for improving properties of bonded magnets by using specific polyamide resins (Japanese Patent Application Laid-Open (KOKAI) Nos. 7-226312(1995), 9-190914(1997), 9-283314(1997), 11-302539(1999), 9-71721(1997), 2000-3809 and 2000-348918, etc.).
At present, it has been strongly demanded to provide resin compositions for bonded magnet having an excellent moldability, and bonded magnets having excellent mechanical strength and heat resistance. However, the conventional resin compositions for bonded magnet and the conventional bonded magnets have failed to satisfy these requirements.
Namely, in Japanese Patent Application Laid-Open (KOKAI) No. 7-226312(1995), there is described the resin composition for bonded magnet, which comprises a polyamide resin having modified end groups. However, in this KOKAI No. 7-226312, the ratio between contents of end carboxyl groups and end amino groups is not taken into consideration, and the resin composition for bonded magnet described therein fails to exhibit an excellent moldability.
In Japanese Patent Application Laid-Open (KOKAI) No. 9-190914(1997), there is described the bonded magnet using a resin mixture composed of a polyamide resin containing a benzene ring in a main chain thereof and another polyamide resin having a melting point of 270xc2x0 C. and a crystallinity of not more than 35%. However, in this KOKAI No. 9-190914, the ratio between contents of end carboxyl groups and end amino groups is not taken into consideration, and the resin composition for bonded magnet described therein fails to exhibit a sufficient moldability.
In Japanese Patent Application Laid-Open (KOKAI) No. 9-283314(1997), there is described the bonded magnet using a polyamide resin obtained from terephthalic acid, a dicarboxylic acid component other than terephthalic acid and a diamine component. However, the ratio between contents of end carboxyl groups and end amino groups is not taken into consideration, and the resin composition for bonded magnet described therein fails to exhibit a sufficient moldability.
In Japanese Patent Application Laid-Open (KOKAI) No. 11-302539(1999), there is described the bonded magnet using a polyamide resin obtained from terephthalic acid and an aliphatic diamine. However, the ratio between contents of end carboxyl groups and end amino groups is not taken into consideration, and the bonded magnet described therein fails to exhibit a sufficient mechanical strength because the aliphatic diamine contains a large amount of linear diamine.
In Japanese Patent Application Laid-Open (KOKAI) Nos. 9-71721(1997) and 2000-3809, there is described the bonded magnet using a polyamide resin containing end carboxyl groups and end amino groups at specific concentrations. However, since end amino groups of the polyamide resin are modified with a carboxyl-containing organic compound, the carboxyl concentration in the resin composition becomes excessively high. As a result, the resin composition for bonded magnet described therein fails to show an excellent recycling property.
As a result of the present inventors"" earnest studies to solve the above problems, it has been found that by using as a binder an aromatic polyamide resin produced from an aromatic carboxylic acid and an aliphatic diamine, which has a molar ratio of residual end carboxyl groups to residual end amino groups ((end carboxyl groups)/(end amino groups)) of 0.1 to 1.0 and a solution viscosity of not more than 1.1 dl/g, the obtained bonded magnet can exhibit excellent mechanical strength and heat resistance. The present invention has been attained on the basis of this finding.
An object of the present invention is to provide a resin composition for bonded magnet which can exhibit excellent moldability and recycling property.
Another object of the present invention is to provide a bonded magnet exhibiting excellent mechanical strength and heat resistance.
To accomplish the aims, in a first aspect of the present invention, there is provided a resin composition for bonded magnet, comprising magnetic particles, and an aromatic polyamide resin produced from an aromatic carboxylic acid and an aliphatic diamine, which aromatic polyamide resin has a molar ratio of residual end carboxyl groups content to residual end amino groups content ((end carboxyl groups)/(end amino groups)) of 0.1 to 1.0 and a solution viscosity of not more than 1.1 dl/g.
In a second aspect of the present invention, there is provided a resin composition for bonded magnet, comprising magnetic particles, and an aromatic polyamide resin produced from an aromatic carboxylic acid and an aliphatic diamine composed of a linear diamine and a branched diamine, which aromatic polyamide resin has a molar ratio of residual end carboxyl groups content to residual end amino groups content ((end carboxyl groups)/(end amino groups)) of 0.1 to 1.0 and a solution viscosity of not more than 1.1 dl/g, a molar ratio of the linear diamine content to the branched diamine content ((linear diamine)/(branched diamine)) being less than 4.0.
In a third aspect of the present invention, there is provided a resin composition for bonded magnet, comprising magnetic particles, and an aromatic polyamide resin produced from an aromatic carboxylic acid and an aliphatic diamine composed of a linear diamine and a branched diamine, which has a molar ratio of residual end carboxyl groups content to residual end amino groups content ((end carboxyl groups)/(end amino groups)) of 0.1 to 1.0 and a solution viscosity of not more than 1.1 dl/g,
a molar ratio of the linear diamine content to the branched diamine content ((linear diamine)/(branched diamine)) being less than 4.0, and
the resin composition having a melt flow rate (MFR) of 70 to 500 g/10 min and a torque increasing time upon kneading in plastomill of 15 to 60 minutes.
In a fourth aspect of the present invention, there is provided a bonded magnet produced by molding a resin composition for bonded magnet, comprising magnetic particles, and an aromatic polyamide resin produced from an aromatic carboxylic acid and an aliphatic diamine, which has a molar ratio of residual end carboxyl groups content to residual end amino groups content ((end carboxyl groups)/(end amino groups)) of 0.1 to 1.0 and a solution viscosity of not more than 1.1 dl/g.
In a fifth aspect of the present invention, there is provided a bonded magnet produced by molding a resin composition for bonded magnet, comprising magnetic particles and an aromatic polyamide resin produced from an aromatic carboxylic acid and an aliphatic diamine, which has a molar ratio of residual end carboxyl groups content to residual end amino groups content ((end carboxyl groups)/(end amino groups)) of 0.1 to 1.0 and a solution viscosity of not more than 1.1 dl/g,
the bonded magnet having an IZOD impact strength of 10 to 20 kJ/m2 and a flexural strength of 100 to 180 MPa.
In a sixth aspect of the present invention, there is provided a bonded magnet produced by molding a resin composition for bonded magnet, comprising magnetic particles and an aromatic polyamide resin produced from an aromatic carboxylic acid and an aliphatic diamine composed of a linear diamine and a branched diamine, which has a molar ratio of residual end carboxyl groups content to residual end amino groups content ((end carboxyl groups)/(end amino groups)) of 0.1 to 1.0 and a solution viscosity of not more than 1.1 dl/g,
a molar ratio of the linear diamine content to the branched diamine content ((linear diamine)/(branched diamine)) being less than 4.0, and
the bonded magnet having an IZOD impact strength of 10 to 20 kJ/m2 and a flexural strength of 100 to 180 MPa.
In a seventh aspect of the present invention, there is provided a resin composition for bonded magnet, comprising magnetic particles, and an aromatic polyamide resin produced from an aromatic carboxylic acid and an aliphatic diamine composed of a linear diamine and a branched diamine, which aromatic polyamide resin has a solution viscosity of not more than 1.1 dl/g,
a molar ratio of the linear diamine content to the branched diamine content ((linear diamine)/(branched diamine)) being less than 4.0.
In an eighth aspect of the present invention, there is provided a bonded magnet produced by molding a resin composition for bonded magnet, comprising magnetic particles, and an aromatic polyamide resin produced from an aromatic carboxylic acid and an aliphatic diamine composed of a linear diamine and a branched diamine, which aromatic polyamide resin has a solution viscosity of not more than 1.1 dl/g,
a molar ratio of the linear diamine content to the branched diamine content ((linear diamine)/(branched diamine)) being less than 4.0.